In the prior art, adjustable oleopneumatic deadened support columns with an oil and air chamber in the column are known. For instance, DE-1529432 (Bilstein) describes an adjustable central oleopneumatic support column, particularly for chairs, comprising: a first tube, the base of which is rigidly connected to the base of a chair, and a second, superior, tube, telescopically inserted into the first and coaxially slidable within it, with its upper end secured under the seat of the chair. An internal command coaxial bar is vertically movable by a lever under the seat, and extends within the first and second tubes. It is associated with first piston means, slidable inside the first tube forming two chambers, respectively an upper chamber and a lower chamber, containing oil, with valve means to allow or to prevent the passage of oil from one chamber to the other, to make height variation possible by means of the actuation of said lever under the seat. Second freely slidable floating piston means in said first tube and under first piston means define and delimit said lower chamber and form a bottom chamber that contains air or compressible gas to offer a spring function.
A second column is described in IT-41632A/85d WO, A1,8807828 in the name of LIFTER SRL. This column provides a similar support with the second tube slidable internally in the first tube. The second piston means are fixed internally within the first tube and the second tube slides inside said second piston means. The bottom chamber presents a lower plug valve for charging and discharging respectively the air chamber pressure. Both the aforesaid prior art columns present substantial structural drawbacks and as such are not practicable or reliable. The first mentioned in particular does not allow an automatic elongation of the column, but for said elongation it is necessary to operate a pull in the open condition of the intercommunication device thereof. This operation is complex and tiresome for the user and overall hindered by the presence of the air chamber that yields elastically. The second column attempts to solve this problem by the presence of the second tube that is immersed as a further piston inside the bottom chamber allowing an auto elongation of the column by an intercommunication open device between the two oil chambers, but this solution presents a complex structure for fixation of the second means to the piston, resolvable only by high production costs particularly for the internal working of the first body.
Further disadvantages of the second solution are caused by a system of small valve means, principally in oil hole passageways where ring seals or gaskets must pass in reciprocation from one chamber to the other, each time that the operator actuates the command lever to lower or to lift the seat, moving such seals across open holes causing the inevitable breaking of same.
Finally, the second device does not present valid axial guide means as in the first, and therefore involves the further damaging of said seals and inevitable misalignment due to oscillation. Furthermore, it is pointed out that the column disclosed in IT-41632A/85 does not provide deadening means, and in the column of DE-1529432 (F. A. August Bilstein) the resistance to elongation causes air infiltrations due to pressure differences created during extraction in elongation of the column. The same problems are raised in EP, A, 343339 (Bansbach, Hermann), being developed substantially in the same way. In fact, EP, A, 343339 discloses one additional piston means below the first piston means. However, the functional effect of the two oil chambers acting as a whole as mentioned in this application is not achieved.
Moreover, in each of the prior art columns described above, there is the presence of a necessarily limited chamber of air. In the first for said second piston means and in the second solution for said second tube that is closed from below and acts as a substantially impenetrable piston stem.
The purpose of the present invention is to eliminate the above mentioned drawbacks.